Attenuated RC tone control circuit

The circuit principle is shown in Figure 1-560. In the figure, RPi is the treble control potentiometer. Because the capacity of C3 and C4 is greater than the capacity of cl and C2
, for high-frequency signals, C4 and C4 can be regarded as short circuits. Therefore, the treble adjustment circuit can be simplified as Figure 1-57.
When the RPi movable arm moves to the uppermost point A, since the resistance of RPi is much greater than Rz, the R PI and C2 branches can be regarded as open circuits,
so Figure 1-57 can be equivalent to Figure 1-58 (a). And because cl can be regarded as an open circuit for bass and midrange, so when
the frequency is relatively low, V2/V1=Child2"Ri+Child2)0 Figure 1-58 (a) For high frequency, q The capacitive reactance of ct is very small, and high-frequency signals
can pass smoothly. Therefore, the volume of t treble is increased compared to the bass. When the frequency is high to a certain extent,
ct can be regarded as a short circuit, and V2 is almost equal to VI. Figure 1- 58 (b) is the lifting characteristic curve of the circuit (a). The solid line in the figure
is the precise value of the control characteristic, and the dotted line is the approximate value. The frequency at which the treble begins to turn is fHI=1/2 rrClRi. From this point
, the frequency increases every When the frequency is doubled, the signal boost increases by about 6dB; when the characteristic curve changes from boost to flat
turning frequency, H2=(Ri+Rz)/2,arRiRzC1. If Ri=10R2, then, =iO When the frequency increases
by 10 times, the voltage transmission ratio will increase by 20dB (10 times).